1. Field of the Invention
Plasma accelerator systems serve, for example, as drives for space missiles. In this connection, a working gas is ionized in a plasma chamber, and the ions are accelerated in an electrostatic field and expelled as a neutralized plasma beam, by means of electrons that are supplied.
2. The Prior Art
The most common embodiment type of such plasma accelerator systems is the so-called Hall thruster, whose ring-shaped plasma chamber has an essentially radial static magnet passing through it. Such Hall thrusters are known, for example, from EP 0541309 A1 or U.S. Pat. No. 5,847,493.
In the case of these Hall thrusters, an electron source arranged outside of the plasma chamber, on the side of its beam exit, and laterally offset relative to the latter, emits an electron stream that is partly passed into the plasma chamber, under the influence of the electric field between the electron source and an anode arranged at the bottom of the plasma chamber, as ionization electrons, and partly carried along by the ions that exit from the chamber, as neutralization electrons. The ionization electrons are deflected in the plasma chamber, under the influence of the magnetic field, and form ring-shaped drift streams, whereby the duration time and the ionization effect on the working gas that is introduced into the plasma chamber is significantly increased.
DE-AS 1222589 shows a plasma accelerator system, in which an arc discharge is ignited in a plasma chamber delimited in length by an anode and a cathode. The resulting ions are drawn off by a ring-shaped ion acceleration electrode arranged outside of the plasma chamber and separated from the latter by an insulated electrode, and expelled in accelerated manner. An energy-rich bundled electron beam supplied from the cathode side, on the center axis of the system, runs through the plasma chamber and exits through the acceleration electrode with the electrons of the electron beam, and neutralizes the ion beam. The electrons that are formed during the arc discharge and the electrons of the supplied beam that are braked by means of pulse processes perform an oscillating movement between the ion acceleration electrode and the cathode. A magnetic collimator field that runs parallel to the longitudinal axis bundles the particle streams about the center axis. Additional electrostatic acceleration stages having magnetic bundling can follow the acceleration electrode.
A plasma accelerator is described in Patent Abstracts of Japan 09223474, which has a plasma generator chamber and a plasma accelerator chamber, one after the other, through which working gas is passed, in each instance. A coil arrangement generates a beam-parallel magnetic field. Several stabilization electrodes that surround the beam are arranged in the two chambers, one after the other.
A plasma accelerator system is known from DE 19828704 A1, in which an energy-rich bundled electron beam is introduced into a plasma chamber delimited, in the longitudinal direction, by an anode and an end electrode, and passed through a magnet arrangement along the center axis. Several intermediate electrodes are provided in the longitudinal direction between the anode and the end electrode, which divide the potential difference between the anode and the end electrode into several stages. The magnet arrangement shows the particular feature that the magnetic field it generates in the plasma chamber periodically changes polarity in the longitudinal direction, and that alternating field segments of the first type and the second type occur in the longitudinal direction, whereby in the segments of the first type, the field lines run predominantly radially, i.e. perpendicular to the longitudinal direction, and in the segments of the second type, the field lines run predominantly axially, i.e. parallel to the longitudinal direction. The segments of the first type preferably lie between two consecutive electrodes, in the longitudinal direction, and form barriers for the electrons accelerated towards the anode. A system structured in this way, in several stages, having the electron barriers, makes it possible to increase the degree of effectiveness of the plasma accelerator. DE 10014033 A1 describes a plasma accelerator system having a similar magnetic field arrangement for a ring-shaped plasma chamber and an electron source that lies on the outside, at the end of the plasma chamber. A plasma accelerator system known from DE 10014033 A1 provides for introduction of the electrons accelerated from the anode side, into a ring-shaped plasma chamber, in the form of a cylindrical hollow beam, into the plasma chamber.
U.S. Pat. No. 6,215,124 B1 describes an ion accelerator according to the type of a Hall thruster, having a ring-shaped plasma chamber and an essentially radial magnetic field between a first magnetic pole that lies radially on the inside and a second magnetic pole that lies radially on the outside. As a particular feature, it is provided here that several electrodes are arranged, in electrically insulated manner, at different radial distances from the exit of the plasma chamber, on the beam exit side of the plasma chamber, at its face that points in the beam direction, which lies essentially crosswise to the beam direction and outside of the plasma chamber, which electrodes lie at different intermediate potentials between the cathode potential and the anode potential, or even below them. A maximum of the longitudinal gradient of the magnetic field is shifted in the direction of the exit of the plasma chamber, and preferably outside it, by means of a magnetic short-circuit about the anode region. A field lens that counteracts the divergence of the ion beam can be generated in the electrostatic acceleration field, by means of the intermediate electrodes on the outside face, and the maximum of the acceleration field can be moved behind the beam exit opening, in the beam direction.